Explicație pas cu pas:
4.
[tex]E = \frac{ \cos^{4} (x) + \sin ^{2}(x) \times \cos^{2} (x) }{ \sin^{2} (x) } = \frac{ \cos^{2}(x)(\cos^{2}(x) + \sin ^{2}(x))}{ \sin^{2}(x) } = \frac{ \cos^{2}(x)}{ \sin^{2}(x) } = ( \frac{ \cos(x) }{ \sin(x) } )^{2} = \cot^{2} (x) [/tex]
5.
[tex]5C0 + 5C1 + 5C2 + 5C3=\frac{5!}{0!5!} + \frac{5!}{1!4!}+\frac{5!}{2!3!}+\frac{5!}{3!2!} = 1 + 5 + 10 + 10 = 26[/tex]
